This should not be a problem. To save a lot of time I will gang similar thickness steel-backed and polyester-backed plates for exposure but then wash them out separately (steel or polyester) because of the configuration of my machine. Main thing I suppose is keeping the exposed plates away from ambient light prior to washout.

Gerald-interestingly enough, a plate I exposed then left 1 hr for lunch was better than one immediately developed/processed-same batch of plates, but also maybe better because first warmed up the lights…….anyways, doing a back lit test on B94F Miraclon a la MacDermid web site-useful place….best w.

I’ve left plates for two days before washing them out with no problem. Just keep them in the dark a few hours will do no harm. Not sure how long you can leave them ultimately, but I used to do this all time. I would gang like 6-7 small plates at a time. Just don’t let them get splashed while you are washing the others - letting water sit on plates that haven’t been post exposed can cause the polymer to curl off the backing.

I’d think that warming up the lamps is good practice but I am not sure how valid it is. Of far more importance I suspect would be warming up the entire operation before you proceed: including bath, machine, raw stock… especially during the winter months. I note that in routine daily operations the bath temp will consistently drop with the first plate and not quite recover. Well, I suppose it might if one was willing to wait around.

There is a bit of latitude in the processing of photopolymer plates. If there were not, DIY operations would not be fruitful.